Obstructive sleep apnea (OSA) is a potentially life-threatening disorder, which affects up to 2-4% of the adult population. OSA, it has been determined, is associated with snoring, which affects 20% of adults. Both of these conditions can be triggered when the base of the tongue collapses during sleep, so that it partly obstructs the airway.
Various methods are known in the art for treatment of snoring and OSA, with varying degrees of success. Generally, the most successful non-surgical approach is continuous positive airway pressure (CPAP), in which a positive pressure is maintained in the airway to prevent blockage. CPAP, however, requires that the patient sleep with a respirator mask over his or her face, with a bedside air compressor to supply positive air pressure to the mask. Because of the discomfort and inconvenience, patient compliance with CPAP therapy is low, and 60% of patients who commence using CPAP stop using the apparatus within three months.
Oral appliances, such as "SnorBan," distributed by SnorBan of Rancho Cordova, Calif., generally operate by holding the patient's jaw forward. These appliances generally require careful fitting, and relatively few patients find them comfortable enough to sleep with them in place through the entire night.
Surgical procedures for treatment of snoring and OSA include uvulo-pharyngeal-palatoplasty (UPPP), midline glossectomy, hyoid suspension and tracheotomy. In UPPP, the lateral portion of the soft palate is removed, a painful procedure with high post-operative morbidity and only partial success. In midline glossectomy, a central, posterior portion of the tongue is removed, which is likewise associated with high morbidity, and requires a perioperative tracheotomy. Hyoid suspension, in which the tongue is pushed forwardly by tying the hyoid bone to the anterior mandible, is somewhat less invasive than the other procedures described, but has in the past been an open surgical procedure that has so far met with limited success. In serious cases of OSA, tracheotomy may be the only currently effective surgical treatment.
European patent application EP 0 743 076 A1, the teachings of which are incorporated herein by reference, describes an apparatus for treatment of sleep apnea by electrical stimulation of a patient's hypoglossal nerve. An electrode is positioned in electrical contact with a portion of the nerve, and a stimulating electrical current is applied to the electrode. The electrical current thus stimulates muscles of the upper airway, so as to cause contralateral extension of the patient's tongue and/or to increase the volume of the oropharynx. The apparatus requires, however, that the electrode be maintained in wired connection with an electronic nerve stimulator unit located outside the body. It also requires accurate and consistent contact with the nerve so as to avoid unwanted tongue movements.